In June (a long time ago) I asked for help for an accordion counter bass
fingering fmt file to be able to _underline_ fingering numbers, indicating
that they have to be played in the counter bass row (Terzbass in german).
As the whole medium is very new to me, it all takes a long time. Now I
hope it works. The tiny little fmt file is to be found at http://www.0-ant.de
It's a bit "the mountain laboured and gave birth to a mouse" but anyway I
am using it quite often.